Recently, rotary electric machines such as an electric motor and an electric generator are mounted in various types of devices and hence they are demanded for higher functionality and smaller size and weight. For instance, an automobile with the limited space for mounting such a rotary electric machine also highly needs a high power and reduced weight electric machine. Regarding such a rotary electric machine, Patent document 1 listed below discloses a stator structure in which coils are placed in slots of a stator core.
FIG. 10 is a plan view showing a part of a stator core disclosed in Patent document 1. A stator core 100 has a cylindrical shape and is formed, on its inner peripheral side, with slots 111 shaped like grooves each extending along an axial direction (vertical to the drawing sheet) of the stator core 100. The slots 111 are arranged in a circumferential direction to provide a plurality of protruding pole pieces 112 each being located between adjacent two of the slots 111. A coil wire is wound around each pole piece 112 by extending between one slot 111 to another slot 111. Herein, a coil is formed of conductor segments 115 which are conducting wires each having a rectangular cross section.
FIG. 11 is an enlarged view of one of the slots 111. This slot 111 is a groove having a rectangular cross section and has protrusions 114 whereby the width of an opening 113 is made narrower than the inner width. An insulator 116 made of an insulating material is inserted in the slot 111. The opening 113 is designed so that an interval 117 (see FIG. 10) between opposite protrusions 114 is slightly wider than the thickness of each conductor segment 115 and the width of the insulator 116 set in the slot 111 is approximately equal to the interval 117. Therefore, in an assembling method for such a conventional stator structure, the insulator 116 is first inserted in the slot 111 and then a predetermined number of the conductor segments 115 are inserted in the slot 111.